This invention relates to ceramic bodies and more particularly to translucent ceramic bodies containing alumina as the main ingredient.
Conventional sintering of alumina involves hydrogen or vacuum firing. For example, U.S. Pat. No. 3,026,177 to St. Pierre et al. discloses the production of a transparent alumina body by subjecting a compact of alumina to a first firing in hydrogen at 1650.degree. C. to 1750.degree. C. to effect removal of gas-containing pores from the body, and subjecting the body to a second firing in hydrogen at 1800.degree. C. to 2000.degree. C. for not less than 15 minutes to remove additional pores and improve the transparency of the body. U.S. Pat. No. 3,026,210 to Coble discloses the production of a high density alumina body having substantial transparency by forming a mixture of alumina powder and a small but effective amount up to 0.5 weight percent of magnesia powder into a compact, and firing the compact at 1700.degree. C. to 1950.degree. C. in vacuum or hydrogen for 2.5 to 4 hours. U.S. Pat. No. 3,905,845 to Kobayashi et al. discloses the manufacturing of translucent polycrystalline alumina body by sintering an alumina compact doped with 0.05-0.5 wt % of yttria, 0.05-0.5 wt % of lanthana, and 0.01-0.1 wt % of magnesia in vacuum, hydrogen, or ammonium decomposed gas at 1600.degree. to 1800.degree. C. for 5 hours. U.S. Pat. No. 4,285,732 to Charles et al. discloses the production of a translucent alumina body by sintering an alumina compact doped with magnesia (0.03 to 0.15 wt %) and an additive selected from ZrO.sub.2 (0.0002 to 0.07 wt %) and HfO.sub.2 (0.003 to 0.12 wt %) in hydrogen at 1750.degree. to 1950.degree. C. for 3 hours. The cost of such firing is high. Hydrogen is an expensive gas, and use of hydrogen further requires that special furnaces equipped with safety provisions be used. In the case of vacuum firing, high-cost vacuum furnaces are required.